Press for hydrostatic extrusion of tubing

ABSTRACT

In the hydrostatic extrusion of tubing, a hollow billet is pressed forward into the conical die opening of the press by a following piston until the material of the billet is pressed inwardly against the mandrel and is shaped to the conical surface of the die, after which pressure fluid is admitted around the billet for hydrostatic extrusion.

United States Patent 1191 Nilsson 1 Apr. 17, 1973 PRESS FOR HYDROSTATIC [56] References Cited EXTRUSION 0F TUBING UNITED STATES PATENTS [75] Inventor: Jan Nilsson, Robertsford, Sweden i 3,531,965 10/1970 Nilsson ..72/60 Asslgneei Allmalma Sven-Ska Elektflska 3,702,556 11/1972 Larker et a] ..72/60 tiebolaget, Vasteras, Sweden [22] Filed; M 1, 1972 Primary Examiner-Richard J. Herbst Appl. No.: 230,726

Foreign Application Priority Data Mar. 15, 1971 Sweden .3280/7l US. Cl ..72/60, 72/264 Int. Cl. B2lc 23/08 Field of Search ..72/60, 264

Attorney-Jennings Bailey, .1 r.

[ 57 ABSTRACT In the hydrostatic extrusion of tubing, a hollow billet is pressed forward into the conical die opening of the press by a following piston until the material of the billet is pressed inwardly against the mandrel and is shaped to the conical surface of the die, after which pressure fluid is admitted around the billet for hydrostatic extrusion.

2 Claims, 3 Drawing Figures PRESS FOR HYDROSTATIC EXTRUSION OF TUBING BACKGROUND OF THE INVENTION 1 Field of the Invention The present invention relates to a press for hydrostatic extrusion of tubing. The press comprises a high pressure cylinder with a high pressure piston at one end and a die at the other end and a mandrel in the cylinder shaft, and a billet holder consisting of an annular piston which seals tightly against the cylinder walland against the outside of the mandrel. The billet holder is provided with a valve means which permits a pressure medium to pass from one side of the billet holder to the other at a certain pressure.

2. The Prior Art The press is of the same type as that described in US. Pat. application Ser. No. 145,184 filed May 20, I971, Nilsson et al. The press is operated by inserting a tubular billet in the cylinder between the die and the billet holder where it is fitted on to the mandrel. The space between the high pressure piston and the billet holder is then filled with a pressure medium and the high pressure piston is then pushed by an operating device into the cylinder to generate the necessary pressure. The pressure medium is pressed through the valve in the billet holder into the space behind this where it surrounds the billet and fills out the space around it. The actual extrusion process can then commence by the pressure medium squeezing the billet in the cylinder.

In order to prevent the pressure medium from leaking out between the mandrel and the hollow of the billet, which would prevent the necessary extrusion pressure from being built up, the billet is drilled with an inwardly projecting collar at the front end, as can be seen from said application, so that the front end of the billet fits tightly around the front end of the mandrel and also against the die.

This means that the front end of the raw billet must be very accurately shaped in order to achieve a reliable start of the process, and it is obvious that this involves added complication and extra costs.

SUMMARY OF THE INVENTION The object of the present invention is to avoid this complication and this is done by setting the valve in the billet holder to such a high pressure that the pressure on the billet holder before the valve opens is enough to upset the front end of the billet so that it seals both against the die and the mandrel before the pressure medium penetrates into the space around the billet. A straight hole can therefore be drilled in the billet, which easily slips over the mandrel without any special collar.

In order to facilitate upsetting of the front end of the billet, this should be shaped so that the upsetting only occurs in a limited zone of the front end around the mandrel and the hole in the die. Even in this case, therefore, the billet must be shaped to a certain extent but in comparison with what was done previously, it does not have to be exactly shaped but should only have roughly the form desired.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be further described with reference to the accompanying drawings in which FIG. 1 shows a press according to the invention, whereas FIGS. 2 and 3 show suitable shapes of the billet.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the press comprising a high pressure cylinder 1 and a high pressure piston 2 which is activated by an operating device, not shown. At the other end of the cylinder is the die 3 which is supported by a flange 4. The entire press is inserted in a press stand, not shown, which also contains the operating device, as is clear from the above-mentioned patent application.

In the cylinder shaft is a mandrel 5 which is fixed in a holder 6 with a drill hole 7 for the pressure medium. The holder 6 rests against the die 3 over a cylindrical tube 8. I

When extrusion is to take place, the die 3 and flange 4 are first removed, after which a billet 1 1 is fitted over the mandrel 5 against a billet holder 9 which slides on the mandrel 5 and fits tightly against the mandrel and the tube 8. The die 3 and flange 4 are then replaced. Pressure medium is supplied through the channel 12 so that it fills the space in front of the piston 2 and through the hole 7 to the billet holder 9. Suitable leakage paths for the air in the system are arranged in a manner not shown.

When the piston 2 is then pressed to the right, the pressure in front of it increases and the billet holder 9 thus presses the front end of the billet 1 1 against the die 3. This front end is thus upset so that it seals both against the mandrel 5 and the die. As this upsetting continues the pressure in the cylinder in front of the piston 2 increases, whereupon the valve 10 in the billet holder opens and the pressure medium fills the narrow spaces between the billet and the cylinder wall. The pressure continues to increase intil the material in the billet 1 1 starts to move, thus initiating the extrusion.

In order to limit the part of the billet which is upset against the die and the mandrel and thus limit the pres sure and the work required for this, only the center of the front end of the billet should at first rest against the die 3. According to FIG. 1 this has been achieved by giving the conical front end of the billet a more acute apex angle than the funnel-shaped inside of the die.

FIGS. 2 and 3 show other embodiments of the billet bearing in mind the above. FIG. 2 shows almost the same shape as FIG. 1, but a small section 13 in the middle has been blunted down to the same angle as that in the die. According to FIG. 3 a portion 14 in the middle has been drawn out to form a pointed nozzle whereas the larger portion 15 of the front end has the same top angle as the die. The most suitable shape depends to a large extent on the material to be extruded.

I claim:

1. Method for hydrostatic extrusion of tubing, in a press comprising a high pressure cylinder (1), a high pressure piston (2) projecting into one end of the cylinder, a die (3) arranged at the other end of the cylinder, a mandrel (5) arranged in the center of the cylinder and a billet holder (9) comprising an annular piston which seals tightly against the cylinder wall and around the outside of the mandrel and is provided with a valve (10) which permits a pressure medium to pass at a certain pressure from one side of the billet holder until the pressure medium passes through the valve and produces extrusion of the billet.

2. Method according to claim 1, in which the die (3) forming part of the press is funnel-shaped on the side facing the billet (11), and the orifice angle in the funnel-shaped part of the die is greater than the apex angle of the main part of the front end of the billet; the front end of the billet being upset to the same angle as the die around the opening (13,14) of the tubular billet. 

1. Method for hydrostatic extrusion of tubing, in a press comprising a high pressure cylinder (1), a high pressure piston (2) projecting into one end of the cylinder, a die (3) arranged at the other end of the cylinder, a mandrel (5) arranged in the center of the cylinder and a billet holder (9) comprising an annular piston which seals tightly against the cylinder wall and around the outside of the mandrel and is provided with a valve (10) which permits a pressure medium to pass at a certain pressure from one side of the billet holder to the other, which comprises inserting a tubular billet (11), the hollow of which passes easily over the mandrel, in the cylinder space between the die and the billet holder and the high pressure cylinder, and thereafter compressing a pressure medium in the cylinder space between the high pressure piston and the billet holder while preventing passage of pressure medium through the valve until the end of the billet facing the die is upset so that the billet tightly surrounds the mandrel, and thereafter increasing the pressure until the pressure medium passes through the valve and produces extrusion of the billet.
 2. Method according to claim 1, in which the die (3) forming part of the press is funnel-shaped on the side facing the billet (11), and the orifice angle in the funnel-shaped part of the die is greater than the apex angle of the main part of the front end of the billet, the front end of the billet being upset to the same angle as the die around the opening (13,14) of the tubular billet. 